Technical Bulletin 91-001 Nitrogen Loading - Cape Cod Commission

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Technical Bulletin 91-001 (FINAL) NITROGEN LOADING April, 1992 Research on golf courses over the last decade has provided some insights into actual nitrogen leaching rates. Brown, et al. (1982) fertilized bermudagrass at a rate of 3 lbs N/1,000 ft 2 of turf and found a leaching rate of 22%. Petrovic (1990) summarized 33 leaching studies conducted in sandy soil and found leaching rates which ranged between 0 and 56.1%. Leaching rates vary with soil type, application rate, precipitation, temperature, turf type, and applied nitrogen forms. Average lawn sizes are also important to determine when application rates are presented in terms of pounds per unit area. The Long Island 208 study of application rates also included a section on lawn sizes, along with surveyors checks of a certain percentage of respondents. This survey found that lawn sizes were fairly constant, averaging 36-40% of total lot size in all categories except extremely low and extremely high densities (NSRPB, 1978). CCPEDC recognized that comparable information was not available for Cape Cod and selected a standard size lawn of 5,000 ft 2 based on a lot size of between 10,000 and 15,000 ft 2 (CCPEDC, 1979). Lawn sizes averaged 4,350 ft 2 in a survey conducted for the Yarmouth Water Resources Protection Study (IEP, 1988). Historically, the WRO staff has used a fertilizer application rate of 3 lbs N/ 1,000 ft 2 /yr with a leaching rate of 60% off an average lawn of 5,000 ft 2 . The application rate and standard lawn size seem to be appropriate in light of the lack of definitive information. However, the research which has been done on leaching rates seems to indicate that the 60% leaching rate figure is too conservative. Petrovic’s work has indicated that controlled applications of fertilizers on healthy turf can substantially reduce leaching rates, sometimes allowing no leaching. Although Petrovic’s work indicates that a percentage lower than 60% can reasonably be chosen, the CCC WRO believes that the objective of protecting groundwater quality should be the main criteria when selecting a standard leaching rate. Therefore, the CCC WRO will use a leaching rate of 25% in all nitrogen loading analyses. This rate recognizes the results of most of the controlled leaching experiments summarized in Petrovic’s work, while acknowledging that fertilizer is often applied to unhealthy turf in an uncontrolled fashion. In summary, future nitrogen loading calculations submitted to the CCC WRO should use an application rate of 3 lbs N/1,000 ft 2 /yr and a leaching rate of 25% off an average lawn area of 5,000 ft 2 . Water Resources Office 8 Cape Cod Commission
Technical Bulletin 91-001 (FINAL) NITROGEN LOADING April, 1992 B.5. Recharge Recharge from precipitation is the only way to dilute NO -N loading on an 3 aquifer-wide basis and provides an important source of dilution for NO -N 3 concentrations on smaller scales. Approximately 45% of annual precipitation on Cape Cod becomes recharge (LeBlanc, et al., 1986). The remainder is either transpired by plants or evaporates back to the atmosphere. Precipitation that falls on impervious surfaces (e.g., roofs, parking lots, roads) may be recharged to the water table at a much higher percentage. Two methods of analysis have been used to estimate the average recharge on Cape Cod. LeBlanc, et al. (1986) used the Thornthwaite and Mather method, which is based largely on precipitation measurements, to calculate average recharge rates of 22 inches per year on western Cape Cod and 18 in/yr on eastern Cape Cod. Recharge at Otis Air Force Base has been estimated as 21 in/yr using the same method (LeBlanc, 1982). G. J. Larson of Michigan State University used a radioisotope method to estimate recharge in Truro at between 11 and 16 in/yr, while the Thornthwaite and Mather method calculated a recharge of between 17.3 and 19.4 in/yr (Knott and Olimpio, 1986; Delaney and Cotton, 1972). Prior nitrogen loading methodologies have been based on conservative recharge rates to ensure a margin of safety when determining concentrations. The original CCPEDC loading methodology assumed a recharge rate of 16 in/yr across all of Cape Cod (CCPEDC and USEPA, 1978). Subsequent loading formulas have also used the same recharge rate (CCPEDC, 1979; Frimpter, et al., 1988). The use of this value may be appropriately conservative for use in calculations on sites in eastern Cape Cod, but is certainly too conservative for western Cape Cod. In consideration of the above studies and the wish to adopt appropriately conservative rates, the CCC WRO staff have decided to utilize the following recharge rates for natural and lawn areas in the following towns: 21 in/yr (Bourne, Falmouth); 19 in/yr (Mashpee, Sandwich); 18 in/yr (Barnstable, Dennis, Yarmouth); 17 in/yr (Brewster, Harwich); 16 in/yr (Chatham, Orleans, Eastham, Wellfleet, Truro, Provincetown). The WRO staff considered not using recharge associated with wastewater flows in areas which receive drinking water supplies from private wells, because water is not imported from a public supply well. The public health concern of so called “short circuiting” between wells and septic systems is a more crucial concern than site specific nitrogen loading in these areas. The wastewater in private well areas is not recycled back to a supply well, but flows with the groundwater from its recharge point towards the groundwater Water Resources Office 9 Cape Cod Commission
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Technical Bulletin 91-001 Nitrogen Loading - Cape Cod Commission

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